Careful Drug Use Helps Prevent Antimicrobial Resistance

Though routinely discussed in human medicine, antibiotic resistance is becoming an issue in the equine world.
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Though routinely discussed in human medicine, antibiotic resistance is rapidly becoming an issue in the equine world, as well. Antimicrobial resistance (AMR) is a type of drug resistance whereby bacteria are able to survive exposure to an antibiotic. It is “inherent to the use of antimicrobials,” according to Harold McKenzie III, DVM, MS, Dipl. ACVIM, associate professor of medicine at Virginia Tech’s Marion duPont Scott Equine Medical Center in Leesburg. “Any time antimicrobials are used, there is an inherent selection process whereby the bacteria exposed to the antibiotic will be inhibited or die, but a few bacteria will likely survive. Ultimately, if this process continues, only resistant bacteria remain.” Due to the frequent use of antimicrobials in humans and animals some bacteria are becoming resistant to many antibiotics, a situation known as multidrug resistance (MDR). In order to slow the development and spread of multidrug-resistant bacteria, it is imperative that all parties involved practice the judicious use of antibiotics.

Resistant bacteria have the ability to change their structure or function so an antibiotic is unable to do what it is designed to do: weaken or kill bacteria to encourage the immune system to destroy them. A difficult conceptual challenge for most owners to understand, says McKenzie, is the idea that the horse itself does not become resistant to antibiotics. Rather, the bacteria within the horse become resistant following exposure to the antibiotic. A horse can be colonized with bacteria that are antibiotic-resistant and exhibit no clinical signs, or he can be infected with antibiotic- resistant bacteria and exhibit signs of infection.

Just like in people, methicillin-resistant Staphylococcus aureus (MRSA), multidrug-resistant Pseudomonas, and other bacteria are real threats to animals that have developed bacterial infections that are antibiotic resistant

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